<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    .red {
        background-color: red;
    }
</style>

<body>
    <button class="red">按钮1</button>
    <button>按钮2</button>
    <button>按钮3</button>
    <button>按钮4</button>
    <script>let bts = document.querySelectorAll('button')
        for (let i = 0; i < bts.length; i++) {
            bts[i].addEventListener('click', function () {
                document.querySelector('.red').className = ''
                this.className = 'red'
            })
        }
    </script>
</body>

</html>